U.S. patent number 4,818,847 [Application Number 06/517,745] was granted by the patent office on 1989-04-04 for apparatus for optically reading printed information.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Masahiro Hara, Atutoshi Okamoto, Tadao Oshima, Toshiyasu Sakai, Hiromitsu Takai, Hiroshi Yamamoto.
United States Patent |
4,818,847 |
Hara , et al. |
April 4, 1989 |
Apparatus for optically reading printed information
Abstract
Apparatus for optically reading printed information by radiating
light onto printed information to be reflected thereby, receiving
the reflected light through an optical system and converting the
image of the reflected light into a corresponding electric signal.
The light source employs red light emitting diodes which radiate
highly bright red light having a wavelength peak at about 660 nm so
that the image sensor can receive a highly contrasting reflected
light from the information printed in black on a white base. The
light source further or alternatively employs infrared light
emitting diodes for radiating the light having a peak wavelength at
about 925 nm so that the image sensor can also received a highly
contrasting reflected light from information printed in black on a
blue or green base.
Inventors: |
Hara; Masahiro (Kariya,
JP), Okamoto; Atutoshi (Chita, JP), Sakai;
Toshiyasu (Kariya, JP), Oshima; Tadao (Obu,
JP), Yamamoto; Hiroshi (Anjo, JP), Takai;
Hiromitsu (Obu, JP) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JP)
|
Family
ID: |
26467295 |
Appl.
No.: |
06/517,745 |
Filed: |
July 27, 1983 |
Foreign Application Priority Data
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Jul 29, 1982 [JP] |
|
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57-132818 |
Aug 19, 1982 [JP] |
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57-144273 |
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Current U.S.
Class: |
235/455;
235/462.21; 235/462.45; 250/553; 250/566 |
Current CPC
Class: |
G06K
7/10881 (20130101); G06K 7/12 (20130101) |
Current International
Class: |
G06K
7/10 (20060101); G06K 7/12 (20060101); G06K
007/10 () |
Field of
Search: |
;235/454,462,463,468,469,465,462,455,472 ;382/59,65
;250/566,568,553 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2307283 |
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Nov 1976 |
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FR |
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53-15210 |
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Apr 1978 |
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JP |
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53-76047 |
|
Jul 1978 |
|
JP |
|
54-12229 |
|
Jan 1979 |
|
JP |
|
55-70168 |
|
May 1980 |
|
JP |
|
55-97668 |
|
Jul 1980 |
|
JP |
|
56-33770 |
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Apr 1981 |
|
JP |
|
Primary Examiner: Trafton; David L.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. Apparatus for optically reading thermally printed information in
the form of a combination of black and white bars formed on a
thermally sensitive white base by thermal printing comprising:
a hand-carried case having an opening at one end thereof;
a light source provided in said case and including first and second
pairs of red light emitting diodes in a row for radiating only red
light at a wavelength of around 660 nanometers to said thermally
printed information through said opening to be reflected
thereby;
said second pair of diodes being disposed in between said first
pair of diodes;
image forming means provided in said case for forming, at a
predetermined position, a reflection image of said printed
information in the reflected light received through said
opening;
sensor means of silcon type provided in said case and having a
spectral sensitivity peak of about 700 nanometers and being
disposed at said predetermined position for converting said
reflection image of said printed information into a corresponding
electric signal, and
means for causing said second pair of diodes to radiate red light
with a lower brightness than the brightness radiated by the first
pair of diodes to radiate side portions of said printed information
at a higher intensity than a central portion thereof for
compensating for different length reflection paths from said side
and central portions to said image sensing means to effect more
uniformity of reflected light across said image sensor means.
2. Apparatus as set forth in claim 1 further comprising:
light diffuser means positioned in front of said first and second
light emitting diode means for diffusing said red light so that the
red light radiated to said thermally printed information is more
equalized.
3. Apparatus for optically reading information printed thermally on
a thermally sensitive white base to form a combination of white
bars and black bars, comprising:
a hand-carried housing provided with an opening at front end
thereof;
a plurality of light sources arranged near said opening in said
case for radiating only red light through said opening, said light
sources including diodes having a light radiation spectrum peak
only at about 660 nanometers;
image forming means arranged behind said light source in said case
for forming, at a predetermined position, a reflection image of
said printed information in the light reflected by said printed
information and received through said opening; and
silicon sensor means provided behind said image forming means in
said case and having a spectral sensitivity peak of about 700
nanometers at said predetermined position in said case for
converting said reflection image of said printed information into a
corresponding electric signal;
said light sources radiating said red light at different
predetermined brightness onto said printed information through said
housing opening to illuminate the outer portions of said printed
information more brightly than a central portion thereof for
compensating for different length reflection paths from said outer
and central portions to said sensor means to effect greater
uniformity of reflected light across said sensor means.
4. Apparatus as set forth in claim 3 further comprising:
a light diffuser arranged between said single light source and said
opening in said housing for diffusing said red lights so that the
red light radiated to said printed information is more
equalized.
5. Apparatus for optically reading bar code information printed in
the form of a combination of black and white bars arranged in
parallel, said apparatus comprising:
a hand-carried housing having an opening adapted to encompass said
bar code information transversely;
a plurality of light emitting diodes provided in said housing in
the vicinity of the opening for emitting only red light at a
wavelength of around 660 nanometers, said light emitting diodes
being arranged in line to radiate the red light to said bar code
information through said opening more intensely at the side
portions of the bar code information than at the central portion of
the same;
image forming means including a lens provided in said housing for
forming a reflection image of said bar code information in the
light reflected by said bar code information and received through
said opening; and
an image sensor provided behind said image forming means in said
housing and having a high spectral sensitivity at around wavelength
of red light from said diodes for converting said reflection image
of said bar code information into a corresponding electrical
signal, whereby the amplitude of the electric signal corresponding
to the reflected light travelling respective different light path
lengths from said side and central portions to said sensor is
stabilized by more intensively illuminating the side portions of
the bar code information.
6. Apparatus according to claim 5, wherein said image forming means
includes:
a planar reflex mirror positioned in the vicinity of the opening of
said housing for directing the light reflected by said bar code
information toward said image sensor.
Description
BACKGROUND OF THE INVENTION
The present invention relates to apparatus for optically reading
printed information such as bar codes, letter or numerical
characters or the like printed on a base such as a label or the
like.
In a conventional reading apparatus of this kind such as disclosed
in Japanese laid-open patent application No. 56-33770 published
Apr. 4, 1981, a tungsten bulb has been used to radiate the light
onto information such as bar codes, numerical or letter characters
or the like printed on a white base so that reflected light
corresponding to the printed information is provided, and an
electronically scanned image sensor has been used to convert the
information image of the reflected light into a corresponding
electric signal.
When the information is printed in black using black ink on a white
base, the reflected light is very contrasting because of high and
low light reflectivities of the white portion and the black
portion, respectively, over a whole range of wavelengths of the
illuminating light from a tungsten bulb. Thus, no disability in
information reading arises.
However, when the information is printed in black using a thermal
printer on a heat sensitive white base, the reflected light becomes
less contrasting as the wavelength of the illuminating light
becomes longer because of the increased light reflectivity of the
black portion in the longer wavelengths of the light. Since the
illuminating light from a tungsten bulb has many infrared light
wavelengths which are longer than the wavelengths of visible light,
the reflected light is not contrasting enough to be read and an
information reading disability is encountered.
For this reason, an infrared light filter which cuts off the
infrared wavelength component has usually been provided to lower
the light sensitivity in the infrared light wavelength range in
view of the fact that the image sensor has a high light sensitivity
in the range of the infrared light wavelengths.
However, even if an infrared light cut-off filter is used, the
cut-off characteristic of the filter is not nullified in the range
of the visible light wavelengths in spite of the considerable
decrease in the wavelength range from the near infrared light to
the visible light. Therefore, the light radiation intensity of a
tungsten bulb must be increased to compensate for the decrease in
the spectral sensitivity due to the filter operation. This results
in a large-sized light source and an increase in the generated heat
issuing from the light source.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide reading
apparatus which can read information printed either by black ink on
a white base or a thermal printer on a heat sensitive white base
without using an infrared light cut-off filter.
It is a further object of the present invention to provide reading
apparatus which can read information printed by ink on a colored
base.
The optical reading apparatus according to the present invention
includes a light source for radiating the light to a printed
information to be reflected thereby, and an image sensor for
receiving the reflected light through an optical system and
converting the image of the reflected light into a corresponding
electric signal. In one embodiment, the light source includes red
light emitting diodes which radiate highly bright red light having
a wavelength at about 660 nm (nanometers) so that the image sensor
can receive a highly contrasting reflected light from information
printed by black ink or a thermal printer on a white base.
The light source further, or alternatively, employs other light
emitting diodes such as infrared light emitting diodes for
radiating the light having a light wavelength at about 925 nm so
that the image sensor receives highly contrasting light reflected
from information printed in black on either a blue or green
base.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a partially schematic view of a first embodiment of the
present invention with parts broken away;
FIG. 2 is an enlarged schematic view of the major portion of the
first embodiment shown in FIG. 1;
FIG. 3 is a characteristic chart used in describing the first
embodiment shown in FIG. 1;
FIG. 4 is a partially schematic view of the second embodiment of
the present invention with parts broken away;
FIG. 5 is a characteristic chart used in describing the second
embodiment shown in FIG. 4;
FIG. 6 is an electric wiring diagram of a portion of the second
embodiment shown in FIG. 4; and
FIG. 7 is an electric wiring diagram of a modification of the
diagram shown in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is now described in greater detail with
reference to the accompanying drawings.
In FIGS. 1 and 2, numeral 1 designates a pair of serially-connected
red light emitting diodes which have a light radiation spectrum
peak at about 660 nm (nanometers) to radiate highly bright red
light having a wavelength of about 660 nm. The diodes 1 are
connected in series with a resistor (not shown) which determines
the light brightness. Numeral 2 designates another pair of
serially-connected red light emitting diodes positioned between the
pair of the light emitting diodes 1 and connected in parallel
therewith. The light emitting diodes 2 which have the same light
radiation characteristic as diodes 1 are connected in series with a
resistor (not shown) having a slightly larger resistance value to
decrease slightly the light brightness thereof relative to that of
the light emitting diodes 1. The diodes 1 and 2 may be a planar
type which planarly radiate the red light. The use of light
emitting diodes 1 and 2 with high brightness is effective to
decrease the heat generated by the light source. Although two
diodes 1 and two diodes 2 are preferable, it is to be understood
that either more or less of each may be employed as desired or
needed in any given situation. In fact, with appropriate lens
arrangements and/or with some types of diodes it may not be
necessary to use any central diode with decreased light output.
A light diffuser 3 is positioned in front of the diodes 1 and 2 to
diffuse and equalize the illumination light irradiated to a white
label 4 on which information to be read is printed.
The information printed on the label 4 is a conventional type bar
code 5 which comprises a combination of white bars and black bars.
Starting with a white base for label 4, the black bars may be
printed thereon conventionally either by black ink or by a thermal
printer (if the label is heat sensitive) which turns the label
black where the heat is applied. As shown in FIG. 2, bar code 5
provides various pieces of information by variations of the widths
of the white bars and the black bars.
Numeral 6 designates a planar reflex mirror which reflects and
changes the direction of the reflected light from the bar code 5
toward a light condensing lens 7 and an iris member 8.
An image sensor 9, which may be a conventional silicon
semiconductor type, is positioned behind the iris member 8 to
receive the reflected light passing through the lens 7 and the iris
member 8 onto the sensor's reading line 9' at which a number of
photo elements (not shown) are aligned to have a one-dimensional
resolution. The image sensor 9 may be a planar type which has a
two-dimensional resolution. The image sensor 9 generally has a
spectral sensitivity peak in the range of 650 through 900 nm.
A hand-carried case 10 made of light shielding material encases the
above-described optical system and has an open head 10' which faces
the label 4 so that the illuminating red light to the bar code 5
and the reflected light from the bar code 5 pass therethrough.
Although not shown, a light shielding member may be provided in the
case 10 to prevent the illuminating light from the diodes 1 and 2
from being received by the image sensor 9 directly or though the
reflex mirror 6, the lens 7 and the iris member 8.
The above-described reading apparatus is connected to a
conventional data processing unit, not shown, through signal cables
which transfer electric signals for electronically scanning the
image sensor 9 and transfer electric signals produced by the image
sensor 9.
The operation of the above embodiment is described next. The
apparatus is first hand-carried to the label 4 as shown in FIG. 1
to encompass the bar code 5 transversely, and the red light
emitting diodes 1 and 2 are all energized to radiate highly bright
red light. The red light is irradiated to the bar code 5 through
the light diffuser 3 and the open head 10' so that the light is
reflected by the bar code 5. As a result of the light reflection,
the transverse image of the bar code reflection is formed, through
the planar reflex mirror 6, the lens 7 and the iris member 8, at
the reading line 9' of the image sensor 9. Since the light
reflectivity of the black bars and the white bars printed on the
label 4 differs from each other, the bar code reflection image
formed on the image sensor 9 has a light density distribution which
corresponds to the bar code 5.
The photo elements of the image sensor 9 are preferably scanned one
by one by the above-mentioned data processing unit (not shown) to
convert the reflected image to an electric signal the successive
amplitudes of which correspond to the successive light densities of
the reflected light representing the color of the bars and the time
durations of which correspond to the widths of the reflected light
representing the widths of the bars of the bar code 5.
It is to be noted that the information reading capability of the
apparatus is dependent on the arithmetic product of the spectral
sensitivity of the image sensor and the contrast of the reflected
light which can be a difference in light reflectivities of the
black bar and the white bar. The use of the light emitting diodes 1
and 2 which radiate red light is advantageous in enhancing the
information reading capability as described next.
In FIG. 3, curve A illustrates the spectral sensitivity
characteristic of the image sensor 9, curve B illustrates the
wavelength distribution characteristic of the red light from the
diodes 1 and 2, and curve C illustrates the light reflectivity
characteristic of black bars printed by a thermal printer.
As an example in FIG. 3, the spectral sensitivity characteristic of
the image sensor 9 is shown by curve A to have a peak value at 700
nm, and the light radiation spectrum distribution of the light
emitting diodes 1 and 2 is shown by curve B to reside in the range
of about 660.+-.30 nm with a peak value at about 660 nm. The light
radiation spectrum distribution of the diodes 1 and 2 may vary in
the range of 660.+-.60 nm depending on the diodes used.
With respect to the light reflectivity of a black bar printed by
the heat sensitive printer, curve C shows it at about 83% (PCS
(printer contrast standard value)=0.02) relative to light having a
wavelength of 900 nm, at about 53% (PCS=0.37) relative to light
having a wavelength of 660 nm and at about 8% (PCS=0.89) relative
to light having a wavelength of 550 nm. Here, the printer contrast
standard value is defined as follows: ##EQU1## Thus, the light
reflectivity of a thermally printed black bar becomes higher as the
wavelength becomes longer, and conversely its light reflectivity
becomes lower as the wavelength approaches that of visible light.
The light reflectivity of a white bar is higher than 70%.
Therefore, it will be understood that light having a shorter
wavelength is more desirable to provide a more contrasting
reflected light.
However, since the peak value of the spectral sensitivity
characteristic of the silicon semiconductor type image sensor 9 is
generally in the range from 650 nm to 900 nm, the spectral
sensitivity of the image sensor 9 is more degraded as the
illuminating light irradiated to the bar code 5 has the shorter
wavelength. The spectral sensitivity of the image sensor 9, for
example is degraded to the range between 80% and 90% at the
wavelength 600 nm. For this reason, it will be understood that
light emitting diodes 1 and 2 having a light radiation spectrum
peak at about 660 nm should be used as the light source of the
reading apparatus in view of both the light reflectivity of the
thermally printed black bar and the spectral sensitivity
characteristic of the image sensor 9.
It is quite clear from FIG. 3 that light emitting diodes 1 and 2
having a light radiation spectrum peak at about 660 nm are also
effective for reading the bar code 5 which is printed by the black
ink on a white label 4, since the light reflectivity of the black
bar is substantially 0% relative to that of the white bar, 70% to
100%.
With respect to the lengths of the light path between the bar code
5 and the reading line 9' of the image sensor 9 at which the
reflection image of the bar code 5 is formed, the length of the
reflection path starting from the end portions of the bar code 5 is
longer than that starting from the central portion of the same.
However, the bar code reflection image formed on the image sensor 9
is more equalized in brightness over the whole range in this
embodiment, because the light radiation intensity of the outside
light emitting diodes 1 which mainly irradiate the outside portion
of the bar code 5 is kept slightly higher, due to the
above-mentioned differential resistances, than that of the inside
light emitting diodes 2 which mainly irradiate the inside portion
of the bar code 5. Thus, the amplitude of the electric signal
produced from the image sensor 9 is stabilized; hence, the
succeeding signal processing is simplified, and highly accurate
information reading is enabled.
Reference is next made to FIG. 4 in which a second embodiment is
illustrated and the same reference numerals are used to designate
the same or similar components as in the first embodiment.
In the second embodiment, a pair of infrared light emitting diodes
2' having a light radiation spectrum peak at about 925 nm are
arranged between a pair of the red light emitting diodes 1 and
connected in parallel therewith. The infrared light emitting diodes
2' radiate infrared light which has the wavelength in the range of
925.+-.30 nm. A rectangular-shaped condensing lens 3' is positioned
in front of the diodes 1 and 2' to converge and equalize the
illuminating light radiated by diodes 1 and 2' onto bar code 5
printed on label 4. Bar code 5 may be printed in black by black ink
on a white, green or blue label 4 or by a thermal printer on a heat
sensitive white label 4. A switching circuit 11 connected to the
diodes 1 and 2' is positioned in the tail end of the hand-carried
case 10, and a manually-operated on-off switch 12 is provided on
the tail end surface of case 10.
As shown in FIG. 6, the switching circuit 11 is connected to switch
12 and to diodes 1 and 2' so that the switching circuit 11
energizes either pair of diodes 1 or 2' by a power supply +V in
accordance with the position of switch 12. However, as shown in
FIG. 7, the diode pairs may be oppositely oriented and switching
circuit 11 may be designed to energize one of the diode pairs 1 and
2' by power sources +V and -V, respectively, in accordance with the
position of the switch 12.
FIG. 5 illustrates a curve D indicative of the wavelength
distribution characteristic of the infrared light emitting diodes
2' and curves E1 and E2 indicative of the light reflectivity
characteristics of blue and green labels 4, respectively, in
addition to curves A, B and C which are also shown in FIG. 3.
When it is desired to read a bar code 5 which is printed by black
ink or by a thermal printer on a white label 4, only the red light
emitting diodes 1 are energized by the switching circuit 11 and the
switch 12 so that only red light without substantially any infrared
light wavelength may be irradiated onto the bar code 5 through the
illuminating lens 3'. In this instance, substantially the same
reading operation can be performed as in the first embodiment and,
therefore, no further description is necessary.
On the other hand, when the black bars of bar code 5 are printed by
black ink on a blue or green label, to read the bar code 5, the
position of the switch 12 is manually changed to cause switching
circuit 11 to energize only the infrared light emitting diodes 2'.
These diodes 2' radiate infrared light onto bar code 5 through the
condensing lens 3'. Since the light reflectivities of the blue bars
and the green bars are high at the infrared wavelength of about 925
nm as illustrated by curves E1 and E2 in FIG. 5, respectively,
relative to that of the black bar the light reflectivity of which
is substantially 0%, a sufficiently contrasting reflection image of
the bar code 5 is formed on the image sensor 9 when the reflected
light is received at the reading line 9' of the image sensor 9
through the planar reflex mirror 6, the condensing lens 7 and the
iris member 8. Therefore, the bar code reflection image can be
converted into an electric signal by the electronically scanned
reading operation of the image sensor 9.
It is to be noted in the second embodiment that, even if both light
emitting diodes 1 and 2' are energized concurrently, reading the
bar code information is still possible, through the information
reading capability of the apparatus may show some slight
degradation or some difficulty in discriminating between black and
white if the black bars are thermally printed since curve C crosses
curve D so high up. In this case, the switching circuit 11 and
switch 12 may be eliminated, or a position added to energize both
diode pairs concurrently which may be especially useful in those
instances where successive bar codes being read may variously have
white or blue or green backgrounds.
It is to be noted further that the second embodiment may be
modified to use other light emitting diodes in dependence on the
colors of the printed information and label. For instance, green
light emitting diodes which radiate highly bright green light
having a wavelength at about 550 nm may be used to read information
printed by black or red ink on a green label and orange light
emitting diodes which radiate highly bright orange light having a
wavelength at about 600 nm maybe used to read information printed
by black or red ink on a yellow label.
The present invention having been described in detail is not
limited thereto, but is limited only by the scope of the following
claims since the described embodiments may be modified without
departing from the spirit of this invention as defined below.
* * * * *